The present invention relates to remote supervisory and controlling systems. More particularly, the invention relates to a system for remotely supervising and controlling loads in time-divisional multiplex transmission of control and monitor data between a central control unit and terminal units each connected to the central control unit through a two-wire line.
In carrying out the remote supervision and control of loads by a host computer, as shown in FIG. 37 and as described in U.S. Pat. No. 4,213,182, loads L.sub.1 to L.sub.n have been controlled directly by a host computer 110 through a media interface 120 and load control processors 121 provided for remote supervision and control. Briefly, the host computer 110 includes a CPU 111 for performing computing operations, a ROM 112 for storing a system program, a RAM 113 for storing user's programs, an I/O 114 for data input/output, a data storage means 115 for storing monitor and control data, a real time clock 116 and a power means 117. After a suitable program for controlling and supervising the loads L.sub.1 to L.sub.n has been stored in the RAM 113, the CPU 111 executes the program to effect data generation for controlling and supervising the loads L.sub.1 to L.sub.n on the basis of the monitor and control data stored in the data storage means 115 and to carry out signal transmission for controlling and supervising the loads L.sub.1 to L.sub.n through the I/O 114 and the media interface 120. The load control processor 121 receives the signal transmitted through the media interface 120 to perform load control and supervision in accordance with instructions from the host computer 110.
In such a prior art system, however, the media interface 120 for supervision and control is controlled directly by the host computer 110, and there has therefore been a problem in that if the host computer 110 becomes faulty for some reason, the entire remote supervisory and controlling system cannot operate, making it impossible to carry out any supervision and control over the loads L.sub.1 to L.sub.n. Further, in the prior art remote supervisory and controlling system, there has been another problem in that it is difficult to connect a plurality of the host computers 110 to the media interface 120, and hence the loads L.sub.1 to L.sub.n cannot be remotely controlled from a plurality of places.